Microprocessor Multi SPI connection

Discussion in 'Embedded Systems and Microcontrollers' started by ilginsarican, Sep 13, 2019.

  1. trevorjjj

    New Member

    Nov 28, 2018
    4
    2
    Read the data sheets for the devices in use, front to back.

    I've never - in untold years - NOT found such crucial information in the data sheets. As someone has already pointed out, there are DYNAMIC aspects to the 'fan-out' on the signal lines - signal frequency for one. However, IF, on absorbing the data you see no immediate red flags, then put it together and try it. Any problems can be addressed with test equipment and analysis only if there ARE problems - I'd rather that than spend days speculating and asking around with nothing to get my hands on.
     
    atferrari and nsaspook like this.
  2. ilginsarican

    Thread Starter Member

    Jul 13, 2017
    91
    2
    Here is the feedback from NXP:

    [​IMG]
     
  3. trevorjjj

    New Member

    Nov 28, 2018
    4
    2
    I was courteous, and offered my 35 years of R+D experience in dealing with such situations.

    Engineers are notorious for 'not reading the instructions' - I know, I'm one of them!

    When it comes to developing a new circuit outside your experience, say a new chip or bus requirement.

    There is no substitute for the manufacturers data for 'guaranteed' circuit parameters and device limitations.

    Whatever...........
     
  4. trevorjjj

    New Member

    Nov 28, 2018
    4
    2
    Ah yes, the alternative pin-function matrix.

    The number of choices is 8, that allows a single byte to bit-select and store the function value.

    As I understand the query, it's a fan-out limitations prediction that's needed.

    The SPI outputs are from dedicated outputs, their drive limits more than cover an SPI input, so no questions there.[?]

    The SPI input deals with 1 signal at at time - whether those inputs are multiplexed (sharing time as individual 'slots') or selected one by one in sequence. The only question I can extract from this arrangement is matching those multiple outputs so that they don't LOAD the signal lines.

    But since output to input is a 1 to 1 connection, it should be treated as such.

    BUT, I WILL read the data sheet on your receiver device, (I'm guessing the outputs are the usual 10-25mA micro outputs.)
     
  5. trevorjjj

    New Member

    Nov 28, 2018
    4
    2
    I should have emphasised the prior mention of series resistors in the multiple signal lines, this is ALWAYS good practice where multiple signal lines share a common destination.
     
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